FALCON-2010 Fix UT errors due to ActiveMQ upgrade

FALCON-2010 Fix UT errors due to ActiveMQ upgrade

Fixed two test failures due to the upgrade:

1. JMSMessageConsumerTest
After upgrade, some messages are consumed faster and so the initial expectation on no message being dequeued right after the message sending doesn't hold. Also confirmed with bvellanki that this kind of tests are flaky and have caused intermittent test errors before. Therefore, removed getTotalDequeueCount assertion. In addition, the expected message consumptions are tested in existing code "Mockito.verify(jobEndService,...".

2. FalconPostProcessingTest
After upgrade, Falcon will run into an error if it tries to delete messages when ActiveMQ service is stopped. Therefore, need to call start before deleting the message during teardown.

Author: yzheng-hortonworks <yzheng@hortonworks.com>

Reviewers: "Balu Vellanki <balu@apache.org>, Venkat Ranganathan <venkat@hortonworks.com>, Pallavi Rao <pallavi@apache.org>"

Closes #169 from yzheng-hortonworks/FALCON-2010

(cherry picked from commit fb4d0b4955429e6cef413ab073814fc800361bd4)
Signed-off-by: bvellanki <bvellanki@hortonworks.com>